Why It's So Hard to Build a Wing-Flapping Flying Machine

The DIY ornithopter video by Jarno Smeets that spread across the Web this week looks like a fake. Here's why the ancient dream of winged human flight is so difficult—but why someone, someday, really could achieve what Smeets claimed to do.

When a man identifying himself as Jarno Smeets uploaded a video to YouTube of himself apparently taking flight with a homemade flapping wing, it immediately went viral and set off a tidal wave of joy and wonderment: He can fly like a bird! Just as quickly, a backlash of derision followed. Impossible, the doubters declared—it's a hoax. And indeed, some deeper reporting and analysis cast serious doubt on the video's authenticity. Finally, he admitted it was a hoax.

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But for a while, the possibility lingered: Humanity's aspiration to become a creature of the air, a dream even older than Icarus, had at last been made reality.

One person who watched the clip with particular interest was Todd Reichert, a newly minted Ph.D. from the University of Toronto Institute for Aeronautical Studies. Reichert headed a team from the university that built a human-powered ornithopter—an aircraft that propels itself by flapping its wings like a bird or a bat. In 2010 Reichert climbed into the craft, the Snowbird, and piloted it on a record-setting flight. He is the rarest of bird imitators: a veteran ornithopter pilot who has actually flapped his way through the air.

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As Reichert watched the Smeets video, his first impression was that it seemed more or less plausible. The wings were a little too short, he thought, and the backpack power unit was a bit too small—but not egregiously so. Then came the takeoff, the moment when the pilot's feet leave the ground and the craft climbs steeply into the air. It was at that moment, Reichert says, that he realized the tape was a fake. "Just at first glance, it's not even close," he says.

To those of us who are not ornithopter pilots, it might not be immediately obvious why this is so. After all, birds can climb even more steeply than Smeets did. So can bats and insects. In fact, winged flight is so easy that it's evolved independently in the animal kingdom at least four times. "A wing can give you better propulsive efficiency than a propeller," Reichert says.

But the way a bird flies is very different from the way a mechanical ornithopter does. Reichert is well aware of this, because the subject of his doctoral thesis was comparing the flight dynamics of animals with those of man-made craft. It turns out that birds are light-years ahead of us humans when it comes to flapping wings. "A bird is constantly changing the shape of its wing as it flies, folding it in on the upstroke and back out on the downstroke," he says. (For an excellent example, check out this video of an eagle owl in flight at 1000 frames per second.) "It also moves the wing faster on the downstroke than the upstroke. So you see them doing all these complicated extra motions, and with each layer of complexity, the bird becomes more and more efficient. An ornithopter wing, in contrast, is just flapping up and down."

That is why Reichert's own ornithopter performance was much less impressive than the video of Smeets the Internet became smitten with this week. (Though Reichert's performance gets bonus points for being, you know, real.) For its record-setting flight, his team towed Snowbird into the air to an altitude of a few feet, then managed to maintain airborne for less than a minute as it flapped along, holding its altitude but gradually losing speed. Not a barn-burning performance by the standards of conventional aviation, perhaps, yet it still ranks as the most impressive human-powered flapping-wing flight so far.

Reichert's wing could have been more efficient, he says, if his team had tried to emulate the complexity of a bird's wing. "The problem is, in engineering that's not the way to go," he says. "You don't want to say, 'Oh, let's add complexity to get efficiency.' "

One obvious way to boost performance, of course, is to add an engine. (Smeets's contraption was purported to include a battery pack and electric actuators.) The history of powered manned ornithopters dates back to 1942, when a German engineer named Adalbert Schmid reportedly built one powered by a 6-hp engine that was able to take off under its own power and fly for 15 minutes. Nathan Chronister, who has been documenting the romance of winged flight for years on his website, The Ornithopter Zone, says that theoretically there's no reason someone couldn't pull off what Smeets claimed to achieve. "It can be done," he says.

But, he says, an actual functioning craft "wouldn't look quite like [Smeets's]." The wing would need to be longer and more rigid for efficiency, and it would need some means of stabilization to keep from tumbling out of the sky. And, he says, it would not be a strap-on wing—"that configuration has shown to be extremely dangerous"—but instead a craft that the pilot can strap into.

Reichert agrees that something like Smeets' contraption could be feasible. "Someone could do this," he says. "But the challenge is so huge. This is not something you could pull off working in your backyard for a couple of months."

Someday, then, someone might actually bring the dream come to life. Jarno Smeets just didn't happen to be the one to pull it off.

Jeff Wise is a contributing editor for Popular Mechanics and the author of Extreme Fear: The Science of Your Mind in Danger. For a daily dose of extreme fear, check out his blog.